1. Field of the Invention
The present invention relates to a battery module, and more specifically to a terminal coupling structure of a battery module.
2. Description of the Related Art
Unlike a primary battery, a secondary battery is rechargeable. Small capacity batteries each having a single unit cell are generally used for various portable electronic devices such as phones, laptop computers, and camcorders. Large capacity batteries each having a plurality of unit cells are generally used as the power source for driving motors, such as those in hybrid electric vehicles.
Secondary batteries may be classified into different types, for example, prismatic and cylindrical batteries, depending on their shape. Single secondary batteries (hereinafter “unit batteries”) are often connected serially to form a large capacity secondary battery (hereinafter “battery module”).
Each of the unit batteries typically includes an electrode assembly having a positive electrode, a negative electrode and a separator between the positive and negative electrodes, a case for housing the electrode assembly and a cap assembly to seal the case. Positive and negative terminals extend to the exterior of the case through the cap assembly and may be connected to the positive and negative electrodes, respectively.
The unit batteries are often arranged such that positive and negative terminals of one unit battery alternate with the positive and negative terminals of an adjacent unit battery. The positive terminal of one unit battery is electrically connected to the negative terminal of the adjacent unit battery by an electrically conductive adaptor to complete assembly of the battery module.
The electrically conductive adaptor are usually fixed on the positive and negative terminals by nuts. For example, the positive and negative terminals may be threaded. After the electrically conductive adaptor is inserted around the positive and negative terminals, the nuts are coupled to the threads to fix the electrically conductive adaptor to the positive and negative electrodes. Therefore, the positive and negative terminals of the adjacent unit batteries are electrically connected to each other.
However, in a conventional battery module, since a contact area between the terminal and the conductive connecting member is relatively small, the contact resistance may be high, resulting in deteriorated current collecting efficiency. Furthermore, in order to reduce the contact resistance between the terminal and the electrically conductive adaptor, sufficient coupling torque must be applied to the nut. However, when the coupling torque surpasses a threshold level, the coupling torque may rotate the terminal, causing the coupling to fail. Therefore, the amount of coupling torque is limited, and sufficient coupling torque may not be able to be applied to the nut.